The present invention relates to a medicament delivery device comprising a housing (16, 18), arranged to accommodate a medicament container (26)； a power unit (64) arranged inside said housing, said power unit comprising a plunger rod (118), a drive spring (120) operably arranged to act on the plunger rod (118) and, which is, upon activation, operably arranged to act on said medicament container (26), an actuator (90) comprising holding elements (94, 100), capable of releasibly holding said plunger rod (118) with said drive spring (120) in a tensioned state, and an actuator sleeve (76) operably connected to said actuator (90) for releasibly locking said holding elements (94, 100) in a holding state； said medicament delivery device further comprising a medicament delivery member guard (34) slidably movable in said housing (16, 18) and arranged to act on said actuator sleeve (76) for setting said holding elements (94, 100) with said actuator sleeve (76) in a first activation state； an activator unit (130) arranged to be manually operated and which is operably connected to said plunger rod (118) for setting said holding elements (94, 100) with said actuator sleeve (76) in a second activation state, wherein said plunger rod (118) is released when both activation states are set. The invention is characterised in an adjuster element (150, 178) operably arranged between said plunger rod (118) and said activator unit (130), which adjuster element (150, 178) has a length dependent on the initial position of the stopper (28) in relation to the initial position of a proximal end of the plunger rod (118).La présente invention concerne un dispositif d'administration de médicament comprenant un boîtier (16, 18) agencé pour recevoir un récipient de médicament (26) ； une unité d'alimentation (64) disposée à l'intérieur dudit boîtier, ladite unité d'alimentation comprenant une tige de piston (118), un ressort d'entraînement (120) disposé fonctionnellement pour agir sur la tige de pi
